This document provides instructions to create a riscv disk image, a riscv boot loader (berkeley bootloader (bbl)) and also points to the associated gem5 scripts to run riscv Linux full system simulations. The boot loader bbl is compiled with a Linux kernel and a device tree as well.
The used disk image is based on busybox and UCanLinux. It is built using the instructions, mostly from here.
Note: All components are cross compiled on an x86 host using a riscv tool chain. We used 88b004d4c2a7d4e4f08b17ee32d2 commit of the riscv tool chain source while building the source (riscv gcc version 10.2.0).
We assume the following directory structure while following the instructions in this README file:
riscv-fs/ |___ gem5/ # gem5 source code (to be cloned here) | |___ riscv-disk # built disk image will go here | |___ riscv-gnu-toolchain # riscv tool chain for cross compilation | |___ riscv64-sample # UCanLinux source | |__linux # linux source | |__busybox # busybox source | |__riscv-pk # riscv proxy kernel source (bbl) | |__RootFS # root file system for disk image | |___ README.md # This README file
We use RISC-V GNU Compiler Toolchain. To build the toolchain, follow the following instructions, assuming you are in the riscv-fs directory.
# install required libraries sudo apt-get install -y autoconf automake autotools-dev curl python3 libmpc-dev libmpfr-dev libgmp-dev gawk build-essential bison flex texinfo gperf libtool patchutils bc zlib1g-dev libexpat-dev # clone riscv gnu toolchain source git clone https://github.com/riscv/riscv-gnu-toolchain cd riscv-gnu-toolchain git checkout 88b004d4c2a7d4e4f08b17ee32d2 # change the prefix to your directory # of choice for installation of the # toolchain ./configure --prefix=/opt/riscv # build the toolchain make linux -j$(nproc)
Update the PATH environment variable so that the following instructions can figure out where to find the riscv toolchain.
export PATH=$PATH:/opt/riscv/bin/
Note: The above step is necessary and might cause errors while cross compiling different components for riscv if other methods are used to point to the toolchain.
Clone the UCanLinux source.
# going back to base riscv-fs directory cd ../ git clone https://github.com/UCanLinux/riscv64-sample
The following sections provide instructions to build both bbl and disk images.
Clone the latest LTS Linux kernel (v5.10):
cd riscv64-sample/ git clone --depth 1 --branch v5.10 https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
To configure and compile the kernel:
cd linux # copy the kernel config from the riscv64-sample # directory (cloned previously) cp ../kernel.config .config # configure the kernel and build it make ARCH=riscv CROSS_COMPILE=riscv64-unknown-linux-gnu- menuconfig make ARCH=riscv CROSS_COMPILE=riscv64-unknown-linux-gnu- all -j$(nproc)
This should generate a vmlinux image in the linux directory. A pre-built RISC-V 5.10 linux kernel can be downloaded here.
To build the bootloader, clone the RISCV proxy kernel (pk) source, which is an application execution environment and contains the bbl source as well.
# going back to base riscv64-sample directory cd ../ git clone https://github.com/riscv/riscv-pk.git cd riscv-pk mkdir build cd build apt-get install device-tree-compiler # configure bbl build ../configure --host=riscv64-unknown-linux-gnu --with-payload=../../linux/vmlinux --prefix=/opt/riscv/ make -j$(nproc) chmod 755 bbl # optional: strip the bbl binary riscv64-unknown-linux-gnu-strip bbl
This will produce a bbl bootloader binary with linux kernel in riscv-pk/build directory. A pre-built copy of this bootloard binary, with the linux kernel can be downloaded here.
Clone and compile the busybox:
# going back to riscv64-sample directory cd ../.. git clone git://busybox.net/busybox.git cd busybox git checkout 1_30_stable # checkout the latest stable branch make menuconfig cp ../busybox.config .config # optional make menuconfig make CROSS_COMPILE=riscv64-unknown-linux-gnu- all -j$(nproc) make CROSS_COMPILE=riscv64-unknown-linux-gnu- install
Next, we will be setting up a root file system:
# going back to riscv64-sample directory cd ../ mkdir RootFS cd RootFS cp -a ../skeleton/* . # copy linux tools/binaries from busbybox (created above) cp -a ../busybox/_install/* . # install modules from linux kernel compiled above cd ../linux/ make ARCH=riscv CROSS_COMPILE=riscv64-unknown-linux-gnu- INSTALL_MOD_PATH=../RootFS modules_install # install libraries from the toolchain built above cd ../RootFS cp -a /opt/riscv/sysroot/lib . # create empty directories mkdir dev home mnt proc sys tmp var cd etc/network mkdir if-down.d if-post-down.d if-pre-up.d if-up.d # build m5 util for riscv and move # it to the root file system as well cd ../../../../ cd gem5/util/m5 scons build/riscv/out/m5 cp build/riscv/out/m5 ../../../riscv64-sample/RootFS/sbin/
Note: the default cross-compiler is riscv64-unknown-linux-gnu-. To change the cross-compiler, you can set the cross-compiler using the scons sticky variable riscv.CROSS_COMPILE. For example,
scons riscv.CROSS_COMPILE=riscv64-linux-gnu- build/riscv/out/m5
Create a disk of 512MB size.
cd ../../../ dd if=/dev/zero of=riscv_disk bs=1M count=512
Making and mounting a root file system on the disk:
mkfs.ext2 -L riscv-rootfs riscv_disk sudo mkdir /mnt/rootfs sudo mount riscv_disk /mnt/rootfs sudo cp -a riscv64-sample/RootFS/* /mnt/rootfs sudo chown -R -h root:root /mnt/rootfs/ df /mnt/rootfs sudo umount /mnt/rootfs
The disk image riscv_disk is ready to use. A pre-built, gzipped, disk image can be downloaded here.
Note: If you need to resize the disk image once it is created, you can do the following:
e2fsck -f riscv_disk resize2fs ./riscv_disk 512M
Also, if it is required to change the contents of the disk image, it can be mounted as:
mount -o loop riscv_disk [some mount directory]
An example configuration using this disk image with the boot loader can be found in configs/example/gem5_library/riscv-fs.py in the gem5 repository.
To run this, you can execute the following within the gem5 repository:
scons build/RISCV/gem5.opt -j`nproc` ./build/RISCV/gem5.opt configs/example/gem5_library/riscv-fs.py
The gem5 stdlib will automatically download the resources as required. Once the simulation has booted you can interact with the system's console via telnet:
telnet localhost <port>
Another option is to use m5term provided by gem5. To compile and launch m5term,
cd gem5/util/term make # compiling ./m5term localhost <port> # launching the terminal
The linux has both login and password set as root.